The present invention relates to improvements in and relating to a mounting structure or construction for mounting a pressure detector utilizing mainly a sensor chip as a pressure sensitive element.
Diaphragm type pressure detectors utilizing a sensor chip as the pressure sensitive element or strain gauge have been widely used for the detection of fluid pressure in pipes.
FIGS. 10 and 11 illustrate diaphragm type pressure detectors as disclosed in the inventors"" Japanese patent applications No. 10-82707 and 10-008841. The pressure detectors each comprise a sensor base 1 for supporting a pressure sensitive element in the form of a sensor chip 2, a diaphragm 3, a diaphragm base 4, a pressure transfer medium (silicone oil) 5, a seal ball 6, output lead pins 7, and a weld 8. If a fluid pressure 10 is applied to sensor chip 2 through diaphragm 3 and pressure transfer medium 5, voltage signals proportional to the pressure from a semiconductor pressure transducer forming the sensor chip 2 are produced at output lead pins 7.
FIGS. 12 and 13 show the pressure detectors of FIGS. 10 and 11, respectively, mounted to measure pressure in a pipeline or the like. FIG. 14 is an enlarged sectional view of a portion A of FIG. 13.
In FIG. 12, a fixture main body 11 has a fluid channel 11b therein, the channel extending from one side of the main body to an opposite side thereof. The main body 11 is mounted between pipe line end sections 52 so that fluid may flow between the end sections via channel 11b. A fluid passage 22 connects with channel 11b and permits pressure in the channel to be applied to diaphragm 3.
A presser member 12 rests on diaphragm base 4 and a bearing 14 rests on presser 12. A threaded clamping element such as a clamping bolt 15 is inserted into a threaded opening in the fixture main body 11 and, as the clamp is tightened, a force acting through bearing 14 and presser 12 pushes diaphragm 4 downward against a metal gasket 17.
In FIG. 13, clamping element 16 presses down on presser member 13 which in turn presses down on the sensor base 1 so that diaphragm 4 is pressed against metal gasket 17.
In both FIGS. 12 and 13, the pressure applied by the presser member 12, 13 creates an air-tight seal, via the metal gasket 17, between the diaphragm 4 and the fixture main body 11. The metal gasket 17 is made of a material that has a high resistance to corrosion and wear, and does not generate dust.
Diaphragm type pressure detectors constructed as shown in FIGS. 10 and 11 can minimize the so-called dead space when mounted on a pipe line or the like. This offers practical advantages in that the gas exchangeability is high and a desired passive state film without spots, and with a uniform thickness, can be formed with relative ease on the gas-contact surface of the diaphragm 3.
The metal gasket 17, being made of a material having a high resistance to corrosion and not prone to generating dust, is almost free from O-ring corrosion-caused problems, unlike the mountings of diaphragm type pressure detectors using an O-ring. However, other problems exist, the most serious problem being fluctuations in measurements attributable to stress, strain or the like on the diaphragm 3.
Diaphragm 3 is very thin, on the order of 0.05 to 0.06 mm. The diaphragm thickness is reduced to raise the pressure detection sensitivity. In such a state as shown in FIG. 12, therefore, stress or strain on the diaphragm 3 inevitably results at the time of tightening clamping bolt 15 when the contact surface of metal gasket 17 is brought into contact with the block lower surface 4f (FIG. 10) of the diaphragm base 4. This changes greatly the stress applied to the sensor chip 2 through silicone oil 5.
Experiments were conducted using a pressure detector with a diaphragm 0.05-0.06 mm thick, about 10 mm in inside diameter, and having a detection pressure range from several Torr to 7 kgf/cm2 abs. The pressure P acting on the diaphragm 3 was high at some Ps=7 kgf/cm2 abs, and the pressure detector was mounted on the fixture main body 11. The output Vs (mv) and temperature characteristics ZTC (% FS/xc2x0 C.) were not much different from those observed when the pressure detector was in a free state, that is, not mounted on the fixture main body 11.
However, in the case where the pressure P applied to the diaphragm 3 was low, for example, Po=0 kfg/cm2 abs, the output Vo changed by more than 5.2 mv when the pressure detector was mounted. (The output was 16.66 mv before the mounting of the pressure detector and 21.86 mv after the mounting.) The temperature characteristics ZTC (% FS/xc2x0 C.), too, greatly fluctuated from 0.162 to 0.719. That is, as far as the output is concerned, differences in measurements are too large. In respect of temperature characteristics, too, fluctuations are too large to compensate. Thus, this pressure detector presents problems when used in practice.
On the other hand, if the peripheral portion of the diaphragm base 4 is formed as shown in FIG. 11, and if the pressure detector is tightened and clamped with the outer circumferential surface 4d of the block of the diaphragm base 4, and the inner circumferential surface 17d of the gasket 17 not in contact with each other (FIG. 14), the magnitude of change xcex94Vo in output before and after the mounting under pressure Po=0 kgf/cm2 abs can be reduced to less than xc2x1 about 3.5 mv. Likewise, the temperature characteristics ZTC (% FS/xc2x0 C.) will come within a range between 0.052 and 0.259. If the pressure detector is mounted on a pipe line etc., the characteristics will be well applicable in practice through a specific correction procedure.
In the mounting construction shown in FIGS. 13 and 14, the magnitude of the change xcex94Vo in output before and after mounting of the sensor will be small. This is because the gasket 17 is placed between the collar lower surface 4c of a collar 4a provided on the diaphragm base 4 and the outer circumferential surface 4d of the thick (about 2 mm) block 4b of the diaphragm base 4, and further because the inner circumferential surface 17d of the metal gasket 17 and the outer circumferential surface 4d of the block 4b are not in contact with each other. Therefore, even if the presser member 13 applies downward pressure on the metal gasket 17 through the sensor base 1 and diaphragm base 4, the upward and downward reaction forces of the metal gasket 17 are all received by the collar 4a of the diaphragm base 4. In other words, almost no strain or stress, resulting from tightening, acts on the diaphragm 3 formed integrally in the block 4b of the diaphragm base 4.
However, it is desirable that the change xcex94Vo in output before and after the mounting of the pressure detector and the temperature characteristic ZTC (%FS/xc2x0 C.), be as small as possible. With the prior art construction or mounting structure shown in FIG. 14, the trouble is that the magnitude of xcex94Vo is still too large.
The main object of the present invention is to solve the above-mentioned problem encountered when the diaphragm type pressure detector having the constitution shown in FIGS. 10 to 14 is actually applied to the pipe line or the like. That is, an object of the invention is to solve the problem of lowered measurement precision, resulting from large changes in output and temperature characteristics caused by differences in stress or strain on the diaphragm, that arise when the pressure detector is mounted in the fixture main body. This object is achieved by improvements in the structure or construction for mounting the pressure detector on the pressure detector fixture main body so that (1) when the pressure detector is fixed in the fixture main body the output and temperature characteristics will be hardly different from those observed when the pressure detector is not mounted, and (2) the pressure detector can be applied to the pipe line etc. without increasing the dead space in the fluid passage.
An object of the invention is to provide a structure or construction for mounting a pressure detector, the pressure detector comprising a diaphragm base provided with a diaphragm and a sensor base fixed to the diaphragm base and having a built-in sensor element that is activated with displacement of the diaphragm base, the pressure detector being inserted in a mounting hole of a fixture main body mounted in a pipe line with a gasket placed under the pressure detector, the pressure detector being pressed and fixed in an air-tight manner in the mounting hole by a presser member inserted in the mounting hole from above, wherein the presser member is brought in contact with a block upper surface 4e of the diaphragm base 4 and the gasket 17 is brought in contact with a block lower surface 4f of the diaphragm base, and a shallow groove 18b in the form of a ring is defined on the block lower surface 4f at a place inward of the portion contacting the metal gasket 17 so that the strain arising from pressing by the presser member 12 is absorbed by the shallow groove 18b. 
Another object of the invention is to provide a structure or construction for mounting a pressure detector, the pressure detector comprising a diaphragm base provided with a diaphragm and a sensor base fixed to the diaphragm base and having a built-in sensor element that is activated with displacement of the diaphragm base, the pressure detector being inserted in a mounting hole of a fixture main body mounted in a pipe line with a gasket placed under the pressure detector, the pressure detector being pressed and fixed in an air-tight manner in the mounting hole by a presser member inserted in the mounting hole from above, wherein the presser member is brought in contact with a block upper surface 4e of the diaphragm base 4 and the gasket 17 is brought in contact with a block lower surface 4f of the diaphragm base, a shallow groove 18a in the form of a ring is defined in the block upper surface 4e at a place inward of a portion contacting the presser member 12, and a shallow groove 18b in the form of a ring is defined on the block lower surface 4f at a place inward of the portion contacting the metal gasket 17 so that the strain arising from pressing by the presser member 12 is absorbed by the shallow groove 18b 
A further object of the invention is to provide a structure or construction for mounting a pressure detector, the pressure detector comprising a diaphragm base provided with a diaphragm and a sensor base fixed to the diaphragm base and having a built-in sensor element that is activated with displacement of the diaphragm base, the pressure detector being inserted in a mounting hole of a fixture main body mounted in a pipe line with a gasket placed under the pressure detector, the pressure detector being pressed and fixed in an air-tight manner in the mounting hole by a presser member inserted in the mounting hole from above, wherein a first step portion 19 and a second step portion 20 are provided in a lower portion of the mounting hole 11a of the fixture main body 11, with the area between a horizontal plane 20b of the second step portion 20 and the lower contacting surface 17b of the gasket 17 serving as a seal portion, a collar 1a being provided on the sensor base 1 of the pressure detector and a collar 4a provided in an upper portion of the diaphragm base 4, the two collars being placed opposite to each other and fixed, in addition, a seal portion between the collar lower surface 4c of the collar 4a of the diaphragm base 4 and the upper contacting surface 17a of the metal gasket 17, and a shallow groove 18c being defined at an inward portion of the collar upper surface 1b of the sensor base 1 and a shallow groove 18d being defined at an inward portion of the collar lower surface 4c of the diaphragm base 4, both in a ring form, the metal gasket 17 having an almost rectangular section and an upper contact face 17a and a low contact surface 17b so strain arising from pressing the collar upper surface 1b of the sensor base 1 by the presser member 13 is absorbed by the shallow grooves 18c, 18b. 
A further object of the invention is to provide a structure or construction for mounting a pressure detector, the pressure detector comprising a diaphragm base provided with a diaphragm and a sensor base fixed to the diaphragm base and having a built-in sensor element that is activated with displacement of the diaphragm base, the pressure detector being inserted in a mounting hole of a fixture main body mounted in a pipe line with a gasket placed under the pressure detector, the pressure detector being pressed and fixed in an air-tight manner in the mounting hole by a presser member inserted in the mounting hole from above, wherein a first step portion 19 and a second step portion 20 are provided in a lower portion of the mounting hole 11a of the fixture main body 11, with the area between a horizontal plane 20b of the second step portion 20 and the lower contacting surface 17b of the gasket 17 serving as a seal portion, a collar 1a being provided on the sensor base 1 of the pressure detector, the collar 1a and an upper surface 4e of the diaphragm base 4 being positioned opposite of each other and fastened, the diaphragm base 4 protruding downward from a diaphragm base block lower surface 4f to form a seal surface 4g with an area between the seal surface 4g and the upper contact face 17a of the metal gasket 17 serving as a seal portion, a shallow groove 18e being defined at an inward portion of the collar upper surface 1b of the collar 1a of the sensor base 1, a shallow groove 18f being defined at an inward portion of the block lower surface 4f of the diaphragm base 4, and shallow grooves 18g, 18h defined opposite to each other at a position upward of the seal surface 4g protruding downward, each in the form of a ring, the metal gasket 17 having an almost rectangular section with an upper contact face 17a and a low contact surface 17b so strain arising from pressing on the collar upper surface 1b of the sensor base 1 by the presser member 13 is absorbed by the shallow grooves 18e, 18f, 18g, 18h. 
Another object of the invention is to provide a pressure sensor mounting construction as described above wherein an outer circumferential portion 24 of the collar 1a of the sensor base 1 and an outer circumferential portion 25 of the block 4b are made of a material with a high hardness.